The objectives are to study the immune mechanisms whereby cells of the intestinal tract are protected against enteric viral infections. Major attention would be given to passive rather than active immunity. The model system to be used would be, primarily, a study of the infection of pigs with transmissible gastroenteritis (TGE) virus which is admirably suited for this purpose. This virus infects the epithelial cells of the small intestines resulting in a loss of enzymatic activity and villous atrophy. Consequently, a maladsorption syndrome with severe diarrhea occurs. Death in newborn pigs approaches 100%. Thus, there are several parameters available for observing this unique intestinal infection. Porcine enteroviruses will also be used for obtaining certain data. The similarities between the intestinal tract of the pig and the human infant suggest the suitability of this model system. Neutralizing antibodies in colostrum and milk, when ingested frequently, can provide protection of piglets against infection with TGE virus and porcine entero-viruses. Further information will be sought on the method of stimulating antibodies of the IgA class in mammary secretion, since such antibodies provide an optimal degree of passive immunity against enteric infection with TGE virus, in contrast to antibodies of the IgG class. Studies will be continued on the possible use of an attenuated TGE virus for providing protection against an intestinal infection with virulent TGE virus. Mammary secretions from sows, infected or immunized with different viral agents administered by different routes, will be gel filtered and the eluates examined for immunoglobulin classes and antibodies. Intestinal contents from passively or actively immune swine will be similarly examined.